MISFIRE DIAGNOSTIC SYSTEM OF ENGINE

PROBLEM TO BE SOLVED: To prevent wrong diagnosis of misfires by eliminating the specific influence of disturbances on the engine speed fluctuations reliably via a simple process. SOLUTION: Differences (VGi-VGi-1) between the output values of an acceleration sensor for sampling times dt in a prescribed period are integrated in S202 to provide a determination parameter X as a criterion of snatches. The determination parameter X is next compared with a determination threshold A in S203. If the determination parameter X is smaller than the determination threshold A, the decision that no engine speed fluctuations are specific to snatches leaves misfire diagnosis to continue. If the determination parameter X is not smaller than the determination threshold A, misfire detection for misfire diagnosis is canceled. When engine speed fluctuations specific to snatches occur by acceleration/deceleration or sudden road surface changes, false misfire detection is thus prevented reliably via such a simple process.